It's not as simple as fitting a micro switch etc as the control box behind the glovebox also is different & I think the wiring is a bit of a nightmare.
There's no physical difference in the mechanism, even newer regulators have the same motors now that screw together rather than the earlier type which are 'peened over'.
I spoke to Autolusso sometime ago about this & one of their technicians gave up trying to retro fit to his car.
The control box is no problem on a phase 2 or late
model phase 1 ( manufactured after April 1997 ). I've already done it!
As part of my climate control retro fit, I looked into a phase 2 N82 to allow the 'MAX' heater control position position to switch on the heated rear window. Planning ahead, I opted for the later N82 that does autodrop as well and killed two birds with one stone as it were. I also fitted the necessary wiring into the doors via the standard door connectors for autodrop whilst I had the dashboard out for the climate control fit.
This is one of the wires being fitted to the driver's side 'A' pillar connector :
The dashboard doesn't have to come out to do this. It was sensible and easier to do it whilst I had the dash out anyway.
I don't know why the AL tech had problems unless he tried with an early phase 1 which would be extremely difficult as they didn't use the N82 integrated controller - they used separate controllers for all the functionality that was combined into the N82. For a late phase 1 it's really easy. There is only one possible pitfall that is very easily
remedied without even needing to cut any wire and is fully reversible. For LHD phase 2 there may be a problem in not having a spare way in the door/'A' pillar connector on the driver's side of the car ( owing to the external temperature sensor in the door mirror ). I've not looked at it in detail, but even this should be resolvable ( the same connectors were used on AD cars so a minor wiring revision could do it ).
As to the mechanism, yes there is a difference. The AD ones have a microswitch near the spring on a bracket that is wired to off when the window is fully up. The microswitch is actuated by a cam on the moving part of the regulator and when the window has moved down far enough, the microswitch trips and the N82 pin then conducts to ground stopping the window moving any further. The latter is why people who fit non autodrop regulators to AD equipped cars find the window can drop all the way down and won't come back up
I have the two wires temporarily connected to ground at the moment to avoid this.
In summary, the only issues are :
1. Finding the relatively rare N82 ( but you can still buy them new ). More will become available of course as the later cars are broken up.
2. A very easy wiring mod ( which may not even be neccessary ) and does not involve cutting wires on P1. LHD P2 may need a little more work on the driver's door/'A' pillar connector.
3. Getting the microswitch details ( needs to be weatherproof with trailing wires ) - preferably identical to factory ones - paying about £5 each instead of £40
£50 to a dealer! )
4. Making the bracket and cam
5. Cutting the hole in the inner door skin to access the cam for adjustment ( fairly easy when you know the size and position ).
That's it really.